Fluorinated polymers have outstanding properties for a wide variety of applications (Fluoropolymers, Wall L. Wiley, New York (1972); Modern Fluoropolymers (1997), Wiley, New York). They exhibit low surface energy, high thermostability and chemical resistance, low friction coefficient, and are resistant to UV. Because of their outstanding properties they find application in many areas including, for example, elastomers, paints and coatings, surfactants, the electronic industry, and others. Therefore, high-performance fluorinated polymers have been receiving considerable attention as interesting advanced materials.
Although a wide range of condensation monomers can be used in processes for preparing fluoropolymers, the use of partially fluorinated monomers is becoming increasingly attractive because it offers the combined benefits of fluorinated groups (low surface tension, chemical resistance, acid resistance, water repellency, etc.) and aromatic polymers (thermal stability, excellent mechanical properties, etc.).
Dolbier et al. in U.S. Pat. Nos. 6,150,499; 5,536,892; 6,392,097; and 5,849,962, disclosed novel ways to prepare octafluoro-[2,2]paracylophane (AF4) and AF4 derivatives. Furthermore, in U.S. Pat. No. 5,841,005, Dolbier et al. disclosed an improved route to prepare AF4 from various different 1,4 bis(halo difluoro methyl)benzene where the halogen is bromo, chloro or iodo.
In U.S. Pat. No. 6,284,933, Dolbier et al. disclosed the synthesis of 1,1′4,4′ tetrafluoro paraxylene (TFPX) and described the use of TFPX-dibromide to make homopolymer of AF4.
Guidotti and Wakselman in the Journal of Fluorine Chemistry, 2005, 126, 445-449 disclose condensation reactions of the mono substituted compounds bromo and (chlorodifluoromethyl)benzene.
Although several fluorinated monomers have been described in the literature, neither p-bis-(chlorodifluoromethyl)benzene nor p-bis(bromodifluoromethyl)-benzene have been reported as monomers from which a condensation polymer is derived. Because of the aromatic nature of p-bis-(chlorodifluoromethyl)benzene and p-bis(bromodifluoromethyl)-benzene the resulting copolymers can have properties similar to poly(aryl ethers), depending on the nature of the comonomer.
Poly(aryl ethers) are tough linear polymers that possess a number of attractive features such as excellent thermal and chemical stability, high glass transition temperatures, good electrical properties, and very good hydrolytic stability. The primary classes of poly(aryl ethers) are poly(aryl ether ketone)s, poly(aryl ether sulfone)s and poly(thio ether)s. They can be synthesized from a variety of starting materials. Over the years, an abundant scientific and patent literature has developed directed to the formation and properties of poly(aryl ethers).
Some early work (U.S. Pat. No. 3,065,205) involves the electrophilic aromatic substitution (viz. Friedel-Crafts) reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether. Another approach later developed involved a nucleophilic aromatic substitution reaction of an activated aromatic dihalide and an aromatic diol (Journal of Polymer Science, A-1, Vol. 5, 1967, pp. 2415-2427; U.S. Pat. No. 4,108,837 and U.S. Pat. No. 4,175,175).
Poly(aryl ether ketone)s (PEK) are linear aromatic polymers that are widely used in products ranging from optical lenses to computer chips because of their strength, thermal durability, and high glass transition temperatures. PEK can be synthesized by electrophilic Friedel-Crafts acylation condensation of 1,4-diphenoxy benzophenone with terephthaloyl chloride. The syntheses are performed as precipitation polycondensations, and the polyketones are obtained in particle form (Macromolecular Chemistry and Physics, 1997, volume 198 (4) pp 1131-1146).
Poly(ether ether ketone) (PEEK) can be prepared from Bisphenol A and difluorobenzophenone. This polymer is highly crystalline, thermally stable, resistant to many chemicals, and very durable.
In the following example, Bisphenol A, in presence of a strong base such as NaOH undergoes a deprotonation step:
and the resulting bisphenolate can be in turn reacted with difluorobenzophenone to form PEEK.
Poly(ether ether sulfone) has a PEEK structure in which the carbonyl group is replaced by a sulfonyl group. Poly(ether ether sulfone), because of its amorphous nature, can be processed at lower temperatures than PEEK. Poly(aryl ether sulfone)s display many desirable characteristics, including: durability, thermal, hydrolytic and dimensional stability, low coefficient of thermal expansion, retention of modulus to temperatures approaching Tg, and radiation resistance.
Poly(phenylenes)sulfide (PPS), a poly(thio ether), is a material of great commercial importance because of its excellent chemical and thermal resistance, fire retardancy properties, and high mechanical strength.
Several routes can be used to prepare poly(aryl ether sulfone) and poly(aryl ether ketone)s. The most common routes involve nucleophilic polycondensation; electrophilic (Friedel-Crafts) route, such as the reaction of diacyl halides with aromatic reaction of diacyl halides with aromatic hydrocarbons, catalyzed by a Lewis acid; and radical nucleophilic substitution. Additional routes have been described in the literature. For example, the Ullman polymerization (U.S. Pat. No. 3,220,910, and Polymer Preprints, Vol. 28, No. 1, pp. 180-182 (1987)) involves the self condensation of a monomer containing both an halogen moiety and an alcohol moiety. Poly(aryl ether)polymers were also prepared by the nickel catalyzed coupling of aryl polyhalides as described in U.S. Pat. No. 4,400,499. The catalyst comprises a nickel compound and at least one ligand such as triarylphosphine; and an aromatic bidentate compound containing at least one ring nitrogen atom.
Among the widely accepted mechanisms for these types of polycondensation are the aromatic nucleophilic substitution SNAr, and the radical nucleophilic substitution SRN1. SNAr is a two step mechanism in which the nucleophile attacks the activated site to form a resonance stabilized arenium ion intermediate, which is usually the rate determining step, followed by the departure of the leaving group and results in reformation of aromaticity in the ring. The groups known to activate SNAr are strong electron withdrawing groups with electronegative atoms that can accept the electron density coming from the nucleophile. On the other hand, the SRN1 mechanism is a well established mechanism and is recognized as one of the primary possible mechanisms in aromatic nucleophilic substitution (Bunnett, J. F, J. Am. Chem. Soc. 1970, 92, 7463; and Bunnett, J. F, Creary, X., J. Org. Chemistry 1974, 39, 3173). SRN1 mechanism and the factors affecting it are further described in a recent publication from Forbes et al. (Macromolecules, 1996, 29, 3081-89; K. Dukes, M. Forbes, A. Jeevarajan, J. DeSimone, R. Linton, V. Sheares).
Depending on the comonomer choice and reaction conditions, the reaction could follow SNAr mechanism, SRN1 mechanism, or there could be in some instances a competition between SNAr and SRN1 mechanisms. (Macromolecules (1993), 26, 3650; Percec, Rinaldi, Litman; “Reductive dehalogenation versus substitution in polyetherification of 4,4′ dihalo diphenyl sulfone with bisphenol A.”)
For example, while it is established that the dominant chain-growth mechanism in PPS preparation is SNAr, Fahey and Ash (Darryl R. Fahey' and Carlton E. Ash, Macromolecules 1991, 24, 4242-4249) note that support for a minor competing SRN1 reaction that might underlie the SNAr mechanism is found when PPS polymerizations are carefully analyzed, and therefore anomalies in the synthesis of PPS should not be overlooked.
Therefore, it is rather difficult to predict that the copolymerization between p-bis-(chlorodifluoromethyl)benzene or p-bis(bromodifluoromethyl)benzene and a diol or dithiol monomer will occur. Rather, the copolymerization between p-bis-(chlorodifluoromethyl)benzene or p-bis(bromodifluoromethyl)benzene and a diol or dithiol monomer requires the selection of specific monomers and specific reaction conditions that favor the polymerization. Furthermore because of the different electronic environment, it is even more difficult to predict the copolymerization success when the halogen atom is on a fluorinated group.